(a) Field of the Invention
The present invention relates to a sensor network and a method of link extension based on time-slot relaying in the sensor network.
(b) Description of the Related Art
A low energy critical infrastructure monitoring network (hereinafter referred to as an ‘LECIM network’) is a network that connects a sensor device that is positioned at the ground, in the ground, underwater, and within a building that are distributed to a wide area, and because the sensor device is positioned at a location at which it is difficult to perform maintenance after installation, the sensor device should operate for several years with an independent power source like a battery and be able to periodically transmit data under a wireless environment having much change.
FIG. 1 is a diagram illustrating a wireless connection between a network coordinator and a sensor device (a near node, a far node, a hidden node, a competition node, and an out of bounds node) constituting an LECIM network. Here, the out of bounds node can receive a frame from the network coordinator, but represents a sensor device that cannot transmit a frame thereof to the network coordinator due to the limit of a transmission range.
In one area LECIM network that is formed with one network coordinator, it is expected that 1000 or more sensor devices exist, generation data of the device is several tens to several hundred bytes, and data is generated within 1 day to within several tens of seconds. Because the network coordinator always uses a power source, the network coordinator has no limitation in a wireless transmission distance and frame transmission, but the sensor device has a limitation in a wireless transmission distance and the number of data frame transmissions. The sensor device minimizes power consumption, should be able to reliably transfer data periodically or at a random moment, and should be able to receive a network configuration control related message from the network coordinator.
Because a coordinator of the LECIM network always uses a power source, the coordinator can increase a transmission distance, but the sensor device has a limitation in use of power and thus cannot increase a transmission distance, so coverage of the LECIM network having a star-topology is determined according to a transmission distance of the sensor device. In network extension by peer-to-peer (P2P) topology, in order for the sensor device to constitute or maintain a network, exchange of a control message is necessary, and when continuously transmitting/receiving a networking protocol for a long term with a limited power source of the sensor device, there is a problem that frequent replacement of a battery or an operation life-span of a monitoring device is shortened.
Because the network is positioned at a difficult location to perform maintenance, in order to operate for several years or more with an independent power source and to stably operate a monitoring network under a wireless environment having much change after installation, a method of configuring a network that can operate the sensor device with low power and increase an arrival distance of a low power wide area monitoring network is necessary.